Can I make variable-sized products (Custom Sized Product)?

You can set your category to custom sizes (this is only available for your own category, not 4over). Once you enable that then your customers will see flat sizes that you offer but they will also be able to select variable sizing.

It will show the variables between the sizes that you entered as your products. For example, you entered 4x6, 5x7, and 5.5x8.5 then your minimum height and width will be 4 and your maximum will be 8.5.